Infertility affects 40-70 million married couples; of those, approximately 40-60% of the infertility problems are attributed to male-related factors that include: low sperm count, abnormal spermatogenesis, and reduced androgen production. The incidence of male infertility cases has increased at an alarming rate resulting in development of a new syndrome --Testicular Dysgenesis Syndrome. The reasons for the increase in testicular abnormalities are not well understood but may be a direct result of genetic or environmental disruption of cell differentiation during testes development. The transcription factor directing testes development is Sry (Sex determining region of the Y chromosome). Sry is hypothesized to initiate testes determination by inducing differentiation of Sertoli cells and initiating morphogenic changes within the testes. The long-range goal of this research is to elucidate the molecular and cellular mechanisms regulating male sex determination and testicular morphogenesis downstream of Sry gene expression. The objective of this proposal, the first step toward attaining our long-range goal, is to identify putative genes that are directly regulated by Sry and their expression pattern during testes differentiation. The central hypothesis of the proposed research is that Sertoli cell differentiation and testes cord formation are induced by Sry and Sry regulated genes. To test the central hypothesis and accomplish the overall objective of this application the following two specific aims are proposed: 1) identify genes regulated by Sry to induce Sertoli cell differentiation; and 2) identify genes downstream of Sertoti cell differentiation that direct testes morphogenesis. The proposed research is innovative, because it takes a direct approach to fill the gaps in the knowledge of genes that direct male sex determination and testes morphogenesis downstream of Sry. This approach is expected to yield the following outcomes: 1) identify genes directly regulated by Sry during initial Sertoli cell lineage differentiation; 2) identify genes directly regulated by Sry directing testes cord formation; 3) associate expression of Sry to potential Sry-regulated genes; 4) provide pilot studies to submit a more extensive R01 grant application on the function of genes regulated by Sry in the testes; and 5) make fundamental contributions to understanding the causes of testicular dysgenesis leading to male infertility.